diff --git a/changelog.txt b/changelog.txt
index 1ed30ae501..6a8e1397b4 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -29,6 +29,7 @@ Template for new versions:
 ## New Tools
 
 - `gui/export-world-map`: New GUI tool to configure world map exports from the embark selection screen.
+- `squads`: adds a "Select all" toggle (and a ``Ctrl-A`` hotkey) to the squads sidebar for selecting all squads at once
 
 ## New Features
 
diff --git a/docs/squads.rst b/docs/squads.rst
new file mode 100644
index 0000000000..732a64d7c1
--- /dev/null
+++ b/docs/squads.rst
@@ -0,0 +1,23 @@
+squads
+======
+
+.. dfhack-tool::
+    :summary: Add a "select all" toggle to the squads sidebar.
+    :tags: fort interface military
+
+When you open the squads sidebar, you can click the checkbox next to each squad
+to select which squads will receive your orders. This tool adds a "Select all"
+toggle below the squad list so you can select (or deselect) all of your squads
+with a single click instead of clicking each squad individually.
+
+The toggle can also be triggered with the ``Ctrl-A`` hotkey while the squads
+sidebar is open.
+
+The widget is enabled by default. You can disable or reposition it with
+`gui/overlay`.
+
+Usage
+-----
+
+There is no commandline interface; the toggle appears automatically in the
+squads sidebar.
diff --git a/squads.lua b/squads.lua
new file mode 100644
index 0000000000..c10da37b18
--- /dev/null
+++ b/squads.lua
@@ -0,0 +1,156 @@
+-- Adds a "select all" toggle to the squads sidebar
+--@ module=true
+
+local help = [====[
+
+squads
+======
+Adds a "Ctrl+a: Select all" toggle button to the squads sidebar panel. When
+activated, all squads are selected; when all squads are already selected,
+activating it deselects them all.
+
+The button is implemented as an overlay widget and can be repositioned or
+disabled via `gui/overlay`.
+
+Usage::
+
+    squads
+]====]
+
+local gui = require('gui')
+local overlay = require('plugins.overlay')
+local widgets = require('gui.widgets')
+
+local if_squads = df.global.game.main_interface.squads
+
+local function all_selected()
+    local sel = if_squads.squad_selected
+    for i = 0, #sel - 1 do
+        if not sel[i] then return false end
+    end
+    return #sel > 0
+end
+
+local function set_all(value)
+    -- don't hijack the hotkey while the user is typing a name
+    if if_squads.entering_squad_nickname or if_squads.entering_cell_nickname then
+        return
+    end
+    local sel = if_squads.squad_selected
+    for i = 0, #sel - 1 do
+        sel[i] = value
+    end
+end
+
+local function toggle_all()
+    set_all(not all_selected())
+end
+
+-- the squads sidebar is docked to the right edge of the screen, but its
+-- vertical layout shifts with the window height, so we anchor ourselves to the
+-- "Create new squad" button, which sits right below the squad list
+local function find_create_squad_button()
+    local dscreen = dfhack.screen
+    local sw, sh = dscreen.getWindowSize()
+    for y = 4, sh - 6 do
+        local line = {}
+        for x = sw - 45, sw - 1 do
+            local tile = dscreen.readTile(x, y)
+            line[#line+1] = tile and tile.ch > 0 and tile.ch < 128
+                and string.char(tile.ch) or ' '
+        end
+        local s, e = table.concat(line):find('Create new squad')
+        if s then
+            return y, sw - 46 + s, sw - 46 + e
+        end
+    end
+end
+
+SquadsOverlay = defclass(SquadsOverlay, overlay.OverlayWidget)
+SquadsOverlay.ATTRS{
+    desc='Adds a "select all" toggle to the squads sidebar.',
+    default_pos={x=-4, y=44},
+    version=1,
+    viewscreens='dwarfmode/Squads',
+    -- hide while the disband confirmation is showing; it shares the
+    -- dwarfmode/Squads focus string so it can't be filtered by viewscreens
+    visible=function()
+        return not df.global.game.main_interface.squads.disband_confirmation
+    end,
+    default_enabled=true,
+    -- anchor on the first tick the panel opens so the widget never flashes
+    -- at the default position; the rescan is gated by a cheap key check
+    overlay_onupdate_max_freq_seconds=0,
+    frame={w=20, h=1},
+}
+
+function SquadsOverlay:init()
+    self:addviews{
+        widgets.HotkeyLabel{
+            view_id='select_all',
+            frame={t=0, l=0},
+            key='CUSTOM_CTRL_A',
+            label='Select all',
+            on_activate=toggle_all,
+        },
+    }
+end
+
+function SquadsOverlay:onRenderBody(dc)
+    -- keep the label in sync with the actual selection so it stays accurate
+    -- when the user clicks individual squad checkboxes
+    self.subviews.select_all:setLabel(
+        all_selected() and 'Deselect all' or 'Select all')
+    SquadsOverlay.super.onRenderBody(self, dc)
+end
+
+function SquadsOverlay:overlay_onupdate()
+    -- the overlay framework persists user-set positions in config.pos; if the
+    -- user has repositioned us away from the default, don't fight them
+    local config = overlay.get_state().config[self.name]
+    if config and config.pos and
+            (config.pos.x ~= self.default_pos.x or
+             config.pos.y ~= self.default_pos.y) then
+        return
+    end
+    -- cheap bail-out: only rescan when something that can move the "Create new
+    -- squad" button changes (squad count, list scroll, window height), and
+    -- only after a successful anchor so a transient miss doesn't stick
+    local _, sh = dfhack.screen.getWindowSize()
+    local scan_key = #if_squads.squad_id * 1000 +
+        if_squads.scroll_position * 10 + sh
+    if scan_key == self.scan_key and self.anchored then return end
+    self.scan_key = scan_key
+    local y, x1, x2 = find_create_squad_button()
+    if not y then
+        self.anchored = false
+        return
+    end
+    -- sit directly above the button, centered on it and nudged right so the
+    -- label text lines up under the squad checkmark column
+    local t = y - 2
+    local sw = dfhack.screen.getWindowSize()
+    local w = self.frame.w or 20
+    local r = sw - math.floor((x1 + x2) / 2) - math.ceil(w / 2) - 2
+    if self.anchored and self.frame.t == t and self.frame.r == r then return end
+    self.frame.t = t
+    self.frame.l = nil
+    self.frame.r = r
+    self.anchored = true
+    self:updateLayout(gui.ViewRect{rect=gui.get_interface_rect()})
+end
+
+OVERLAY_WIDGETS = {select_all=SquadsOverlay}
+
+if dfhack_flags.module then
+    return
+end
+
+local args = {...}
+if args[1] == 'help' or #args > 0 then
+    print(dfhack.script_help())
+    return
+end
+
+print('The squads sidebar select-all toggle is managed by the overlay framework.')
+print('Use "gui/overlay" to reposition or disable it.')
diff --git a/test/overlay/squads.lua b/test/overlay/squads.lua
new file mode 100644
index 0000000000..3790141467
--- /dev/null
+++ b/test/overlay/squads.lua
@@ -0,0 +1,139 @@
+local gui = require('gui')
+local overlay = require('plugins.overlay')
+
+local if_squads = df.global.game.main_interface.squads
+
+config = {
+    target = 'squads',
+    mode = 'fortress',
+}
+
+local was_overlay_enabled = overlay.isEnabled()
+
+local function get_widget()
+    overlay.setEnabled(true)
+    overlay.rescan()
+    overlay.overlay_command({'enable', 'squads.select_all'})
+    if not overlay.isOverlayEnabled('squads.select_all') then
+        qerror('could not enable squads.select_all overlay')
+    end
+    return overlay.get_state().db['squads.select_all'].widget
+end
+
+local function count_selected()
+    local n = 0
+    for i = 0, #if_squads.squad_selected - 1 do
+        if if_squads.squad_selected[i] then n = n + 1 end
+    end
+    return n
+end
+
+local function feed_keys(keys)
+    gui.simulateInput(dfhack.gui.getCurViewscreen(true), keys)
+end
+
+local function panel_is_open()
+    return dfhack.gui.matchFocusString('dwarfmode/Squads',
+        dfhack.gui.getDFViewscreen(true))
+end
+
+local function set_panel_open(open)
+    if panel_is_open() ~= open then
+        feed_keys'D_SQUADS'
+    end
+end
+
+local function with_squads_panel(test_fn)
+    expect.gt(#if_squads.squad_id, 0,
+        'test fort must have at least one squad')
+    local saved_sel = {}
+    for i = 0, #if_squads.squad_selected - 1 do
+        saved_sel[i] = if_squads.squad_selected[i]
+    end
+    local was_open = panel_is_open()
+    dfhack.with_finalize(
+        function()
+            set_panel_open(was_open)
+            for i = 0, #saved_sel - 1 do
+                if_squads.squad_selected[i] = saved_sel[i]
+            end
+            overlay.setEnabled(was_overlay_enabled)
+        end,
+        function()
+            set_panel_open(true)
+            expect.true_(panel_is_open())
+            for i = 0, #if_squads.squad_selected - 1 do
+                if_squads.squad_selected[i] = false
+            end
+            test_fn(get_widget())
+        end)
+end
+
+function test.select_all_hotkey_selects_all_squads()
+    with_squads_panel(function()
+        expect.eq(0, count_selected())
+        feed_keys{CUSTOM_CTRL_A=true}
+        expect.eq(#if_squads.squad_id, count_selected())
+    end)
+end
+
+function test.select_all_hotkey_deselects_all_squads()
+    with_squads_panel(function()
+        feed_keys{CUSTOM_CTRL_A=true}
+        expect.eq(#if_squads.squad_id, count_selected())
+        feed_keys{CUSTOM_CTRL_A=true}
+        expect.eq(0, count_selected())
+    end)
+end
+
+function test.select_all_click_toggles()
+    with_squads_panel(function(widget)
+        -- compute the widget's frame rect so mouse hit-testing works
+        local sw, sh = dfhack.screen.getWindowSize()
+        widget:updateLayout(gui.ViewRect{rect=gui.mkdims_wh(0, 0, sw, sh)})
+        -- position the mouse inside the widget frame and click
+        local rect = widget.frame_rect
+        df.global.gps.mouse_x = rect.x1 + (widget.frame_parent_rect and widget.frame_parent_rect.x1 or 0) + 1
+        df.global.gps.mouse_y = rect.y1 + (widget.frame_parent_rect and widget.frame_parent_rect.y1 or 0)
+        feed_keys{_MOUSE_L=true}
+        expect.eq(#if_squads.squad_id, count_selected())
+        feed_keys{_MOUSE_L=true}
+        expect.eq(0, count_selected())
+    end)
+end
+
+function test.widget_hidden_during_disband_confirmation()
+    with_squads_panel(function(widget)
+        local getval = require('utils').getval
+        expect.false_(if_squads.disband_confirmation)
+        expect.true_(getval(widget.visible))
+        dfhack.with_finalize(
+            function()
+                if_squads.disband_confirmation = false
+            end,
+            function()
+                if_squads.disband_confirmation = true
+                expect.false_(getval(widget.visible))
+                -- hidden widgets must not consume the hotkey
+                feed_keys{CUSTOM_CTRL_A=true}
+                expect.eq(0, count_selected())
+            end)
+    end)
+end
+
+function test.widget_tracks_external_selection_changes()
+    with_squads_panel(function(widget)
+        -- the label should reflect selection changes made outside the widget
+        local label = widget.subviews.select_all
+        widget:onRenderBody()
+        expect.eq('Select all', label.label)
+        if_squads.squad_selected[0] = true
+        widget:onRenderBody()
+        expect.eq('Select all', label.label)
+        for i = 0, #if_squads.squad_selected - 1 do
+            if_squads.squad_selected[i] = true
+        end
+        widget:onRenderBody()
+        expect.eq('Deselect all', label.label)
+    end)
+end